SHANGHAI, March 12 (Reuters) - The pound jumped and Asian shares rallied on Tuesday after the European Commission agreed to changes in a Brexit deal ahead of a vote in the British parliament on a divorce agreement.

European Commission head Jean-Claude Juncker agreed to additional assurances in an updated Brexit deal with British Prime Minister Theresa May on Monday, but warned UK lawmakers would not get a third chance to endorse it.

Sterling, which had risen ahead of the talks between May and Juncker, extended gains in hopes the changes may be enough to sway rebellious British lawmakers who have threatened to vote down May's plan again on Tuesday.

The pound was up 0.5 percent, buying $1.3215 and taking its gains over two days to more than 1.5 percent.

A lower likelihood of crashing out of the EU with no Brexit deal could help to inject some bullish sentiment into equity markets by eliminating one of the three major concerns of global investors, alongside trade and slowing global growth, said Greg McKenna, strategist at McKenna Macro.

"Take Brexit off the table and I think some of the real money flows that appear to have turned up late last week are likely to be there again. So I think it helps change the backdrop a little bit," he said.

MSCI's broadest index of Asia-Pacific shares outside Japan was up 1.08 percent, with early gains reinforced by a rise in Chinese shares and oil companies, which were buoyed by higher oil prices.

Despite slowing domestic economic growth and uncertainty about the outlook for trade negotiations between China and the United States, Chinese markets have been buoyed this year by investors' expectations of more stimulus to cushion any downturn.

The CSI300 index has risen more than 25 percent this year.

But Oliver Jones, market economist at Capital Economics cautioned that the Chinese rally is "built on shaky foundations."

"The surge in China's mainland equity markets since the start of the year looks excessive, even allowing for renewed optimism about stimulus in China and the possibility of a US-China trade deal," he said in a note.

"Since we are anticipating more economic weakness in both China and the rest of the world regardless, we suspect that the Shanghai and Shenzhen markets will fall back sharply later in the year."

Australian shares were up 0.4 percent, while Japan's Nikkei stock index jumped 1.9 percent, helped by a weaker yen.

The amended Brexit deal gave a further boost to investors' appetite for riskier assets, after global equity indexes climbed overnight on gains in technology stocks and expectations of more stimulus from China.

The Dow Jones Industrial Average rose 0.79 percent, with gains tempered by a 5.3 percent drop in Boeing shares after some airlines grounded the company's new 737 MAX 8 passenger jet following a second deadly crash of the airliner in five months.

The S&P 500 gained 1.47 percent to 2,783.3.

RISING YIELDS

The market's turn toward riskier assets lifted yields on U.S. Treasury bonds, with benchmark 10-year Treasury notes at 2.6645 percent compared with its U.S. close of 2.641 percent on Monday.

The two-year yield was at 2.4998 percent compared with a U.S. close of 2.477 percent.

The dollar index, which measures the greenback against a basket of rivals, shed 0.2 percent to 97.036. But rising risk appetite weighed on the safe-haven yen, pushing the dollar up 0.16 percent to 111.37.

The euro was up 0.13 percent on the day at $1.1262.

In commodity markets, oil prices rose on a combination of strong demand and supply cuts by the Organization of the Petrolum Exporting Countries (OPEC).

A political and economic crisis in OPEC-member Venezuela is also seen as lifting crude prices.

Venezuela's opposition-run congress on Monday declared a "state of alarm" over a five-day power blackout that has crippled the country's oil exports and left millions of citizens scrambling to find food and water.

U.S. crude was up 0.5 percent at $57.08 a barrel and Brent crude was 0.4 percent higher at $66.84.